Short take: The Worm Within is a very enjoyable read. I recommend it and look forward to the next installment.

Long take: I won't describe the plot in details, but it's pretty standard stuff for anyone who's read a smidgen of pulp fantasy and/or sat on fantasy and science-fantasy role-playing game sessions. There's a young apprentice with a mysterious past, a paladin, a magician of sorts, a thief, and a dark threat that puts the whole wold in danger. Still, Sarah Newton manages to inject enough energy in these over-used formulas to keep The Worm Within interesting.

The short chapters, organized around brief sections showcasing Newton's resolute writing style, give the story a strong forward momentum almost from the get-go. There's little to no fat either: the novel's very well edited, with less than a handful of typos.
Jargon pertaining to the world in which the story takes place fills the text, but I never found it so distracting that I stopped enjoying the read. In fact, as the story progressed, said jargon drew me in further.
The Worm Within contains memorable, well-drawn characters. Although the novel's plot-driven, the people we get to spend time with never feel like after-thoughts. It is in fact our concern for their fate that makes The Worm Within such a fun read. As the novel reaches its climax, so too do the emotionally-charged threads tying all the characters together. The result is a very satisfying climax, one that's emotional as well as awesome in scale.
Finally, there's the world, which is one of the novel's main strengths: it's vast and resplendent, full of far-out deep history where super-advanced technology functions alongside awe-inspiring sorcery. If anyone's interested in what the world of Newton's (as of right now up-coming) role-playing game Chronicles of Future Earth might be about, short of buying the game, The Worm Within stands as your best introduction to it. It's pretty clear that there's going to be enough in that game to satisfy some of the most demanding RPG- hobbyists out there: weird creatures, magic, high-tech, weird customs, evil fiends, long lost ruins full of wonders and dangers. Just pure, unadulterated, pulpy fun.

Note: The Worm Within is also the name of the good adventure that appears in Chaosium's 2011 Chronicles of Future Earth supplement. The novel and the adventure have very little in common though, beyond their common title and one of their plot-points. So, dive in.